Method for transmitting and receiving reference signal in wireless communication system

ABSTRACT

The present disclosure relates to a 5G or pre-5G communication system to be provided for supporting a data rate higher than that of a 4G communication system, such as LTE, and subsequent communication systems. The present disclosure relates to a method for transmitting a reference signal (RS) in a wireless communication system, comprising the steps of: configuring a transmission resource by including at least one resource block (RB), which does not map the RS, between two RBs, which map the RS, in a first subframe; transmitting a first message for directing an RB offset indicating a gap between the two RBs, which map the RS, and locations of the RBs, which map the RS; and transmitting the RS through the configured transmission resource.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/510,675,which is the National Stage of International Application No.PCT/KR2015/009587, filed Sep. 11, 2015, which claims priority to KoreanPatent Application No. 10-2014-0119958, filed Sep. 11, 2014, thedisclosures of which are herein incorporated by reference in theirentirety.

BACKGROUND 1. Field

The present disclosure relates to a method for transmitting a referencesignal (RS) in a wireless communication system, and more particularly,to a method for reducing overhead during RS transmission and reception.

2. Description of Related Art

To satisfy the growing demands for wireless data traffic sincecommercialization of a 4^(th) generation (4G) communication system,efforts have been made to develop an improved 5^(th) generation (5G) orpre-5G communication system. That is why the 5G or pre-5G communicationsystem is called a beyond 4G network communication system or a post longterm evolution (post LTE) system.

To achieve high data rates, deployment of the 5G communication system ina millimeter wave (mmWave) band (for example, 60 GHz) is underconsideration. In order to mitigate propagation path loss and increase apropagation distance in the mmWave band, beamforming, massive multipleinput multiple output (massive MIMO), full dimensional MIMO (FD-MIMO),array antenna, analog beamforming, and large-scale antenna technologieshave been discussed for the 5G communication system.

Further, to improve a system network, techniques such as evolved smallcell, advanced small cell, cloud radio access network (cloud RAN),ultra-dense network, device-to-device (D2D) communication, wirelessbackhaul, moving network, cooperative communication, coordinatedmulti-point (CoMP), and interference cancelation have been developed forthe 5G communication system.

Besides, advanced coding modulation (ACM) techniques such as hybrid FSKand QAM modulation (FQAM) and sliding window superposition coding(SWSC), and advanced access techniques such as filter bank multi carrier(FBMC) and non-orthogonal multiple access (NOMA), and sparse codemultiple access (SCMA) have been developed for the 5G communicationsystem.

To increase the system capacity of a wireless communication system,techniques for increasing the number of antennas in a base station (BS)have been developed. A multi-antenna system may increase system capacitysignificantly by facilitating multi-user MIMO (MU MIMO) transmissionthrough an array gain of antennas.

For implementation of a multi-antenna system, a transmitter (forexample, a BS) needs channel information about a receiver (for example,a user equipment (UE)) to which the transmitter is to transmit a signal.In a frequency division dulplex (FDD) wireless network, the receiverestimates channel information and then feeds back the estimated channelinformation to the transmitter in order to provide channel informationneeded for the transmitter. Specifically, the receiver estimates channelinformation using a reference signal (RS) received on a downlink,quantizes the estimated channel information, and feeds back thequantized channel information to the transmitter.

In a long term evolution-advanced (LTE-A) system, the receiver useschannel state information RSs (CSI-RSs) for channel estimation. TheCSI-RSs are designed to use resources orthogonal between antennas, foraccurate channel estimation. Due to the orthogonal feature of theCSI-RSs, more antennas are available in the LTE-A system. However, moreresources are also used for CSI-RS transmission in proportion to anincrease in the number of antennas.

SUMMARY

If a transmitter maps CSI-RSs for all antenna ports to each resourceblock (RB) for estimation of channel information about a receiver in awireless communication system, the accuracy of channel measurementincreases. However, the receiver should feed back channel informationabout all of the antenna ports to the transmitter, and the transmittershould allocate resources for all of the antenna ports. The resultingincrease of overhead reduces resources to be used for data transmission.According to 3^(rd) generation partnership project (3GPP) Release 12, ifinterference between CSI-RSs is ignored, up to 40 resources, that is, 40resource elements (REs) are available for CSI-RSs in one RB. The maximum40 resources may be used for CSI-RS transmission, up to 8 resources perBS, and also for controlling CSI-RS interference between adjacent BSs.However, if the number of CSI-RSs to be used in a BS is increased, thisresource use method needs to be modified. That is, if a system isdesigned so that the maximum number of CSI-RSs to be used per BS may beincreased, 40 resources as provided in the current specification (thatis, 3GPP Release 12) may not be sufficient, considering control ofinterference between adjacent BSs.

An aspect of the present disclosure is to provide a method forincreasing the number of RSs transmitted in radio resources by a basestation (BS) in a wireless communication system.

Another aspect of the present disclosure is to provide a method forsaving resources used in CSI-RS transmission, while minimizing thedegradation of channel estimation performance in a wirelesscommunication system.

Another aspect of the present disclosure is to provide a method forenabling transmission of more RSs, while minimizing the overhead of RStransmission in a wireless communication system.

In an aspect of the present disclosure, a method for transmitting areference signal (RS) in a wireless communication system includesconfiguring transmission resources by including at least one resourceblock (RB) to which an RS is not mapped between two RBs to which RSs aremapped in a first subframe, transmitting a first message indicating aspacing between the two RBs to which RSs are mapped, and an RB offsetindicating positions of the RBs to which RSs are mapped, andtransmitting the RSs in the configured transmission resources.

In another aspect of the present disclosure, a method for transmittingan RS in a wireless communication system includes configuringtransmission resources by mapping at least two different RS subsets ofan RS set, respectively to at least two contiguous RBs in a firstsubframe, transmitting a first message indicating a maximum number ofantenna ports used for transmission of RSs, and transmitting the RSs inthe configured transmission resources.

In another aspect of the present disclosure, an apparatus fortransmitting an RS in a wireless communication system includes acontroller for controlling configuration of transmission resources byincluding at least one RB to which an RS is not mapped between two RBsto which RSs are mapped in a first subframe, transmission of a firstmessage indicating a spacing between the two RBs to which RSs aremapped, and an RB offset indicating positions of the RBs to which RSsare mapped, and transmission of the RSs in the configured transmissionresources, and a transceiver for transmitting the first message and theRSs under control of the controller.

In another aspect of the present disclosure, an apparatus fortransmitting an RS in a wireless communication system includes acontroller for controlling configuration of transmission resources bymapping at least two different RS subsets of an RS set, respectively toat least two contiguous RBs in a first subframe, transmission of a firstmessage indicating a maximum number of antenna ports used fortransmission of RSs, and transmission of the RSs in the configuredtransmission resources, and a transceiver for transmitting the firstmessage and the RSs under control of the controller.

In another aspect of the present disclosure, a method for transmitting achannel state information interference measurement (CSI-IM) in awireless communication system includes configuring transmissionresources by including at least one RB to which a CSI-IM is not mappedbetween two RBs to which CSI-IMs are mapped in a first subframe,transmitting a first message indicating a spacing between the two RBs towhich CSI-IMs are mapped, and an RB offset indicating positions of theRBs to which CSI-IMs are mapped, and transmitting the CSI-IMs in theconfigured transmission resources.

In another aspect of the present disclosure, a method for transmitting aCSI-IM in a wireless communication system includes configuringtransmission resources by mapping at least two different CSI-IM subsetsof a CSI-IM set, respectively to at least two contiguous RBs in a firstsubframe, transmitting a first message indicating a maximum number ofantenna ports used for transmission of CSI-IMs, and transmitting theCSI-IMs in the configured transmission resources.

In another aspect of the present disclosure, a method for feeding back achannel estimation result using an RS in a wireless communication systemincludes receiving a first message indicating a spacing between two RBsto which RSs are mapped, and an RB offset indicating the positions ofthe RBs to which RSs are mapped, receiving the RSs using the spacing andthe RB offset indicated by the first message, performing channelestimation using the received RSs, and feeding back a result of thechannel estimation.

In another aspect of the present disclosure, a method for feeding back achannel estimation result using an RS in a wireless communication systemincludes receiving a first message including information about a maximumnumber of antenna ports used for RS transmission, receiving RSs usingthe maximum number of antenna ports indicated by the first message,performing channel estimation using the received RSs, and feeding back aresult of the channel estimation. The RSs are received in transmissionresources configured by mapping at least two different RS subsets of aset of the RSs respectively to at least two contiguous RBs in a firstsubframe.

In another aspect of the present disclosure, an apparatus for feedingback a channel estimation result using an RS in a wireless communicationsystem includes a controller for controlling reception of a firstmessage indicating a spacing between two RBs to which RSs are mapped,and an RB offset indicating the positions of the RBs to which RSs aremapped, reception of the RSs using the spacing and the RB offsetindicated by the first message, channel estimation using the receivedRSs, and feedback of a result of the channel estimation, and atransceiver for receiving the first message and the RSs, and performingthe feedback, under control of the controller.

In another aspect of the present disclosure, an apparatus for feedingback a channel estimation result using an RS in a wireless communicationsystem includes a controller for controlling reception of a firstmessage including information about a maximum number of antenna portsused for RS transmission, reception of RSs using the maximum number ofantenna ports indicated by the first message, channel estimation usingthe received RSs, and feedback of a result of the channel estimation,and a transceiver for receiving the first message and the RSs, andperforming the feedback, under control of the controller. The RSs arereceived in transmission resources configured by mapping at least twodifferent RS subsets of a set of the RSs respectively to at least twocontiguous RBs in a first subframe.

According to an embodiment of the present disclosure, the systemoverhead of channel state information reference signal (CSI-RS)transmission may be reduced.

According to an embodiment of the present disclosure, more than 8CSI-RSs per base station (BS) may be supported simply by making aminimal modification to a communication scheme conforming to 3^(rd)generation partnership project (3GPP) Release 12.

According to an embodiment of the present disclosure, the accuracy ofchannel measurement may be increased by changing a resource block (RB)offset, and frequency selectivity may be measured indirectly based onfeedback information.

According to an embodiment of the present disclosure, CSI-RS mapping maybe more flexible than in a legacy method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C illustrate a method for supporting transmission of aplurality of channel state information reference signals (CSI-RSs) in alegacy CSI-RS transmission method;

FIG. 2 illustrates a method for mapping CSI-RSs with a spacing betweenresource blocks (RBs) according to an embodiment of the presentdisclosure;

FIGS. 3A-3B illustrate change of CSI-RS transmission positions over timeaccording to an embodiment of the present disclosure;

FIGS. 4A-4B illustrates adjustment of CSI-RS interference betweenadjacent cells using the foregoing embodiment according to an embodimentof the present disclosure;

FIG. 5 illustrates a method for mapping CSI-RSs to a bundle of adjacentRBs according to an embodiment of the present disclosure;

FIG. 6 illustrates a method for mapping a fixed number of CSI-RSs toeach RB according to an embodiment of the present disclosure;

FIG. 7 illustrates a method for applying different CSI-RS mappings todifferent subframes using a plurality of CSI processors according to anembodiment of the present disclosure;

FIG. 8 illustrates a method for applying different CSI-RS mappings tothe same subframe using the foregoing embodiments according to anembodiment of the present disclosure;

FIG. 9 illustrates a method for applying the foregoing embodiment tomapping of CSI-RSs and CSI interference measurements (CSI-IMs) to RBsaccording to an embodiment of the present disclosure;

FIG. 10 is a diagram illustrating a signal flow of a transmitter, whenthe embodiments of the present disclosure are applied;

FIG. 11 is an exemplary block diagram of a transmitter according to thepresent disclosure; and

FIG. 12 is an exemplary block diagram of a receiver according to thepresent disclosure.

DETAILED DESCRIPTION

A representative embodiment for achieving the above technical objectswill be presented in a detailed description of the present disclosure. Adetailed description of a generally known function or structure of thepresent disclosure will be avoided lest it should obscure the subjectmatter of the present disclosure. Although the terms used in the presentdisclosure are defined in consideration of functions in the embodimentsof the present disclosure, the terms may be changed according to theintention of a user or an operator, or customs. Therefore, the presentdisclosure should be understood, not simply by the actual terms used butby the meanings of each term lying within.

Instead of the term ‘antenna’, ‘antenna port’ will often be usedhereinbelow. This implies that an antenna port is not necessarily aphysical antenna in the long term evolution (LTE) wireless accessstandards. In fact, an antenna port is defined by the existence of areference signal (RS) specific to the antenna port. Therefore, if thesame RS is transmitted through a plurality of physical antennas, areceiver does not distinguish them from each other, considering thephysical antennas to be one antenna port. In the present disclosure, theterm ‘channel state information reference signal (CSI-RS) antenna port’may also be interchangeably used.

In the present disclosure, a transmitter is an apparatus fortransmitting an RS such as CSI-RS. For example, a transmitter may referto an apparatus such as a base station (BS) in a cellular communicationsystem.

In the present disclosure, a receiver is an apparatus for receiving anRS such as CSI-RS. For example, a receiver may refer to an apparatussuch as a user equipment (UE) in a cellular communication system.

Further, ‘CSI-RSs are mapped to a resource block (RB)’ means specifyingresource elements (REs) of the RB to be used for the CSI-RSs in thepresent disclosure.

FIGS. 1A-1C illustrate a method for supporting transmission of moreCSI-RSs than defined in a current specification according to anembodiment of the present disclosure.

FIG. 1A is a view illustrating exemplary mapping of a maximum supportednumber of CSI-RSs for one antenna port to an RB according to the currentspecification (that is, 3^(rd) generation partnership project (3GPP)Release 12).

According to 3GPP Release 12, one antenna port may be mapped to up to 8REs in one RB. For example, FIG. 1A is based on the assumption that fourRBs 100, 102, 104, and 106 are transmitted in one subframe. Atransmitter maps eight CSI-RSs 110, 112, 114, and 116 to each of thefour RBs 100, 102, 104, and 106 and transmits the CSI-RSs 110, 112, 114,and 116 to a receiver. A requirement for CSI-RSs is that the CSI-RSs aretransmitted only in specific orthogonal frequency division multiplex(OFDM) symbols to facilitate transmission power control. If all CSI-RSsare mapped to each RB, the accuracy of channel estimation may beincreased. However, if the number of CSI-RSs is also increased due to anincrease in the number of antenna ports, mapping of all CSI-RSs to eachRB may increase system overhead.

A method for transmitting CSI-RSs for more antenna ports using a currentCSI-RS transmission method is to modify a resource configuration thatlimits the number of CSI-RSs to 8. Specifically, FIG. 1B illustrates amethod for transmitting 16 CSI-RSs 130, 132, 134, and 136 extended from8 CSI-RSs, and FIG. 1C illustrates a method for transmitting 32 CSI-RSs150, 152, 154, and 156 extended from 8 CSI-RSs.

Since CSI-RS is an RS used for channel measurement, system operation ispossible without transmitting CSI-RSs in every subframe. In 3GPP Release12, a subframe and the positions of REs which carry CSI-RSs may be setby setting a subframe configuration and a resource configuration. Foroperation of a UE, a BS should indicate a CSI-RS port number, a subframeconfiguration, and a resource configuration to the UE.

A resource configuration for CSI-RS mapping configures a maximum of 40resources for CSI-RSs. The reason for configuring more than 8 resourcesis to enable a neighbor BS to also transmit CSI-RSs in orthogonalresources.

To render CSI-RS reception to be reliable between adjacent cells, eachBS may not transmit data in overlapped RS resources. For this purpose, aresource configuration and a subframe configuration which are related tozero powered CSI-RSs (ZP-CSI-RSs) may be indicated. ZP-CSI-RSinformation may be interpreted in correspondence with one RB, and the UEmay perform data demodulation by applying the interpreted ZP-CSI-RSinformation to all RBs.

Now, a detailed description will be given of various embodiments of thepresent disclosure with reference to the attached drawings.

FIG. 2 illustrates a method for mapping CSI-RSs with a spacing betweenRBs according to an embodiment of the present disclosure.

In the embodiment, an ‘RB spacing’ is an interval between RBs to whichCSI-RSs are mapped. Therefore, an RB spacing is calculated by adding 1to the number of RBs without CSI-RSs between RBs with CSI-RSs mapped.For example, if one RB without CSI-RSs is interposed betweenCSI-RS-mapped RBs, the RB spacing is 2. If there is no RB withoutCSI-RSs between CSI-RS-mapped RBs (that is, if a legacy CSI-RS mappingmethod is used), the RB spacing is 1. In another example, if CSI-RSs aremapped to RB 0, no CSI-RSs are mapped to RB 1, RB 2, RB 3, and RB 4, andCSI-RSs are mapped to RB 5, the RB spacing may be 5.

Therefore, CSI-RSs are mapped to only one of as many contiguous RBs asan RB spacing in the embodiment. An ‘RB offset’ refers to the positionof an RB to which CSI-RSs are mapped. If CSI-RSs are mapped to the firstof as many contiguous RBs as an RB spacing, the RB offset is 0. In FIG.2, since CSI-RSs are mapped in the first RB counted from the top (alongthe frequency axis), the RB offset is 0. In another example, if CSI-RSsare mapped to the third RB and then the eighth RB, the RB spacing is 5and the RB offset is 2.

FIG. 2 illustrates an example based on the assumption that four RBs 200,210, 220, and 230 are transmitted in one subframe 240. Although CSI-RSs250 and 260 are mapped to the first and third RBs 200 and 220, noCSI-RSs are mapped to the second and fourth RBs 210 and 230. That is,CSI-RSs are mapped with an RB spacing of 2 and an RB offset of 0 in theexample of FIG. 2.

Compared to the legacy method, the above proposed embodiment may reducethe overhead of CSI-RS transmission by setting an RB spacing. Atransmitter may change an RB spacing and an RB offset over time, forsystem optimization. The RB spacing and the RB offset may be signaledindependently (that is, as separate information) or as a single combinedvalue.

[Table 1] illustrates an example of combining an RB spacing and an RBoffset into a single value (that is, D_(CSI-RS)).

TABLE 1 RB spacing and RB offset in combination RB offset (CSI-RS RB(CSI-RS-RBSpacingConfig) RB spacing offset) (D_(CSI-RS)) (F_(CSI-RS),RBs) (Δ_(F,CSI-RS)) 0 1 — 1-2 2 D_(CSI-RS)-1 3-5 3 D_(CSI-RS)-3 6-9 4D_(CSI-RS)-6 10-14 5 D_(CSI-RS)-10 15-20 6 D_(CSI-RS)-15

In the example of FIG. 2, the RB spacing is 2 and the RB offset is 0.Therefore, the result of combining the RB spacing and the RB offset,D_(CSI-RS) is 1 because D_(CSI-RS)−1=0. In another example, if the RBspacing is 4 and the RB offset is 2, the result D_(CSI-RS) of combiningthe RB spacing and the RB offset. D_(CSI-RS) is 8 becauseD_(CSI-RS)−6=2.

[Table 2] illustrates an exemplary structure of a message in which thetransmitter transmits CSI-RS information to the receiver according to anembodiment using an RB spacing.

TABLE 2 CSI-RS-Config ::= SEQUENCE {  csi-RS     CHOICE {   release    NULL,   setup     SEQUENCE {    antennaPortsCount ENUMERATED {an1,an2, an4, an8, an16,         an32},    resourceConfig INTEGER (0. .31),   subframeConfig  INTEGER (0. .154),    D-CSI-RS INTEGER (0. .20),   } }

According to the message of [Table 2], the transmitter may add an16 andan32 as values available as antennaPortsCount in order to support 16antenna ports and 32 antenna ports. Further, D-CSI-RS indicating theresult D_(CSI-RS) of combining an RB spacing and an RB offset may beadded.

The transmitter may transmit no signal in specific resource elements(REs) to reduce CSI-RS interference with a neighbor cell. Thetransmitter may transmit information indicating the absence of anysignal in the REs as a ZP-CSI-RS value to the receiver.

Conventionally, the same CSI-RSs are mapped to each RB, and thus thetransmitter transmits ZP-CSI-RSs of a 16-bit bitmap generated based onone RB. On the other hand, if the embodiment using an RB spacing isapplied, the ZP-CSI-RS transmission rule should be changed in case aneighbor transmitter may use a different RB spacing from that of thetransmitter.

For example, it is assumed that transmitter #1 transmits CSI-RSs with anRB spacing of 1, transmitter #2 transmits CSI-RSs with an RB spacing of2, and transmitter #3 transmits CSI-RSs with an RB spacing of 3. Becauseadjacent transmitters use different CSI-RS resource use patterns, theymay have different RB spacings, and thus transmit CSI-RSs at differentpositions according to the RB spacings.

A transmitter needs to apply ZP-CSI-RSs only to CSI-RS resources inwhich a neighbor transmitter transmits CSI-RSs. In the above example,transmitter #1 and transmitter #2 may transmit, to receivers, ZP-CSI-RSinformation with an RB spacing of 3 as well as ZP-CSI-RS informationwith an RB spacing of 1 and ZP-CSI-RS information with an RB spacing of2 not to interfere with CSI-RS transmission of transmitter #3. As aconsequence, resources may be used more efficiently.

That is, the receiver connected to transmitter #1 receives as manypieces of ZP-CSI-RS information as the RB spacing of transmitter #3being a transmitter having a largest RB spacing among the neighbortransmitters. In the example, the receiver receives three pieces ofZP-CSI-RS information which are applied with an RB spacing of 3.

Therefore, the embodiment proposes that a transmitter transmits, to areceiver connected to the transmitter, a plurality of pieces ofZP-CSI-RS information including ZP-CSI-RS information for an RB spacingapplied to the transmitter.

[Table 3] illustrates an exemplary structure of a message in which thetransmitter transmits ZP-CSI-RS information to the receiver according toan embodiment using an RB spacing.

TABLE 3   CSI-RS-ConfigZP ::= SEQUENCE { csi-RS-ConfigZPId    CSI-RS-ConfigZPId,  resourceConfigList     BITSTRING (SIZE (16)),  subframeConfig      INTEGER (0. .154),  ... }csi-RS-ConfigZPId ::= INTEGER (1. .maxRBSpacing)

Although a legacy ZP-CSI-RS bitmap may still be used, an independentZP-CSI-RS bitmap (resourceConfigList) is required for each RB spacing.csi-RS-ConfigZPID may be added to the message in order to reflect anindependent ZP-CSI-RS bitmap for each RB spacing. The ZP-CSI-RS bitmapis information indicating a resource configuration for resources mappedto ZP-CSI-RSs.

Hereinbelow, embodiments of changing an RB spacing and an RB offset overtime for system optimization will be described.

FIGS. 3A-3B illustrate change of CSR-RS transmission positions over timeaccording to an embodiment of the present disclosure.

FIG. 3A illustrates a part of RBs in a subframe that a transmittertransmits to a receiver at time t₀ (t=t₀). The RB spacing is 2 and theRB offset is 0 at time t₀. In other words, CSI-RSs 304 are mapped to RB0 300 among as many contiguous RBs 300 and 302 as the RB spacing.

FIG. 3B illustrates a part of RBs in a subframe that the transmittertransmits to the receiver at time t₁ (t=t₁). The RB spacing is 2 and theRB offset is 1 at time t₁. In other words, CSI-RSs 304 are mapped to RB1 312 among as many contiguous RBs 310 and 312 as the RB spacing.

FIGS. 3A-3B illustrate a case in which the transmitter changes an RBoffset over time, for system optimization. While FIGS. 3A-3B illustratean embodiment of changing an RB offset, the transmitter may change an RBspacing over time. According to the embodiment, the accuracy of channelmeasurement may be increased by changing an RB offset, and the channelstate of a user may be measured indirectly based on changed channelinformation.

FIGS. 4A-4B illustrate adjustment of CSI-RS interference betweenadjacent cells by applying an embodiment using an RB spacing accordingto an embodiment of the present disclosure.

FIG. 4A illustrates a part of RBs that a transmitter transmits to areceiver in cell 1 406, and FIG. 4B illustrates a part of RBs that atransmitter transmits to a receiver in cell 2 416 neighboring to cell 1406.

Cell 1 406 maps CSI-RSs to RBs with an RB spacing of 2 and an RB offsetof 0. That is, CSI-RSs 404 are mapped to RB 0 400 among as manycontiguous RBs 400 and 402 as the RB spacing.

Cell 2 416 maps CSI-RSs to RBs with an RB spacing of 2 (equal to the RBspacing of cell 1 406) and an RB offset of 1 different from that of cell1 406 in order to maintain orthogonality with the CSI-RSs of cell 1 406.That is, CSI-RSs 414 are mapped to RB 1 410 among as many contiguous RBs410 and 412 as the RB spacing.

The foregoing embodiment may offer more flexibility to CSI-RS mappingthan the legacy method, and require application of the same overheadbetween transmission points (for example, BSs or radio remote heads(RRHs)) in a coordinated multi-point (CoMP) set.

FIG. 5 illustrates a method for mapping CSI-RSs to a bundle of adjacentRBs according to an embodiment of the present disclosure.

On the assumption that a BS has 64 antenna ports and should alsotransmit 64 CSI-RSs, mapping of all of the 64 CSI-RSs to every RBincreases system overhead. Therefore, the embodiment proposes a methodfor mapping CSI-RSs across a plurality of adjacent RBs by bundling theRBs. In the embodiment, the BS maps CSI-RSs distributedly to a pluralityof RBs, instead of mapping all of the CSI-RSs to one RB. That is, the BSmaps different subsets of CSI-RSs 540, 550, 560, and 570 respectively toa plurality of RBs 500, 510, 520, and 530 that form an RB bundle. In thepresent disclosure, an RB bundle is a group of contiguous RBs acrosswhich a CSI-RS set is mapped, or a group of contiguous RBs to whichdifferent CSI-RS subsets are mapped. An ‘RB bundle size’ or an ‘RBbundle spacing’ is the number of RBs grouped into one bundle.

In FIG. 5, the total number of CSI-RSs is 64, the RB bundle size is 4,and the number of CSI-RSs mapped to each RB is 16 (= 4/64).

The transmitter may control at least one of an RB bundle size and thenumber of CSI-RSs to be mapped per RB, for system optimization.Therefore, the transmitter should explicitly indicate to the receiver atleast one of the RB bundle size and the number of CSI-RSs to be mappedper RB. Optionally, the transmitter may indicate the positions of mappedCSI-RSs to the receiver.

[Table 4] illustrates an exemplary structure of a message in which thetransmitter transmits CSI-RS information to the receiver according to anembodiment using an RB bundle.

TABLE 4 CSI-RS-Config ::= SEQUENCE {  csi-RS     CHOICE {   release     NULL,   setup     SEQUENCE {    antennaPortsCount ENUMERATED {an1,an2, an4, an8,             an16, an32, an64},    resourceConfig INTEGER(0. .31),    subframeConfig INTEGER (0. . 154),    RBBundingConfig    INTEGER (1, 2, 3, 6),    antennaPortCountPerRB ENUMERATED {an1, an2,an4, an8} }

According to the message, the transmitter supports 16, 32, and 64antenna ports. Thus, an16, an32, and an64 may be added as valuesavailable as antennaPortsCount. Further, RBBundlingConfig representingan RB bundle size and antennaPortCountPerRB representing the number ofantenna ports (that is, the number of CSI-RSs) to be mapped per RB maybe added. According to the message, 1, 2, 3, and 6 may be supported asthe RB bundle size, and 1, 2, 4, and 8 may be supported as the number ofantenna ports to be mapped per RB.

In the embodiment, the transmitter transmits a bitmap for a ZP-CSI-RSresource configuration on an RB bundle basis as a method fortransmitting ZP-CSI-RSs which are information indicating no signal in anRE.

[Table 5] illustrates an exemplary structure of a message in which thetransmitter transmits ZP-CSI-RS information to the receiver according toan embodiment using an RB bundle.

TABLE 5 CSI-RS-ConfigZP ::= SEQUENCE {  csi-RS-ConfigZPId  CSI-RS-ConfigZPId,  RBBundleConfig    INTEGER (1, 2, 3, 6), resourceConfigList   BIT STRING (SIZE (16)*RBBundleConfig), subframeConfig    INTEGER (0. .154),  ... }

RBBundleConfig representing an RB bundle size and resourceConfigListrepresenting a ZP-CSI-RS bitmap may be added to the message. Accordingto the embodiment, the ZP-CSI-RS bitmap may have a size of the productbetween the RB bundle size and the legacy size of one RB (16 bits).

In the embodiments using an RB spacing and the embodiments using an RBbundle, the following may be additionally considered in determining anRB spacing and an RB bundle size.

If a transmitter (for example, a BS) transmits CSI-RSs in RBs to areceiver (for example, a UE), upon receipt of the CSI-RSs, the receivermay perform a procedure of estimating a channel, generating informationabout the estimated channel, and feeding back the information to thetransmitter. Two methods for generating estimated channel informationand transmitting the channel information to a transmitter may beavailable. One of the methods is wideband feedback in which channelinformation about total RBs is generated as a singe piece of informationduring generation of the estimated channel information, and the othermethod is subband feedback in which total RBs are divided into aplurality of subbands and channel information is generated andtransmitted for each subband.

In a system using subband feedback, when feeding back channelinformation about a subband to a transmitter, a receiver may select oneof the factors of the number of RBs per subband (hereinafter, referredto as a ‘subband size’) as an RB bundle size or an RB spacing. Forexample, an LTE system using a frequency bandwidth of 10 MHz mayconfigure the total frequency bandwidth with 50 RBs. According to [Table6], if subband feedback is used in the LTE system, the subband size is 6RBs. Therefore, according to the embodiment, the system may have theconstraint that the RB bundle size or the RB spacing is one of thefactors of 6, that is, 1, 2, 3, or 6. Along with a change in thefrequency bandwidth of the system, a subband size (that is, the numberof RBs per subband), an RB bundle size, and an RB spacing may bechanged, and thus the constraint may also be changed.

TABLE 6 Number of RBs for system bandwidth (NL_(RB) ^(DL)) Subband size(k) 6-7 NA  8-10 4 11-26 4 27-63 6  64-110 8

FIG. 6 illustrates a method for mapping a fixed number of CSI-RSs to oneRB according to an embodiment of the present disclosure.

In FIG. 6, on the assumption that 8 CSI-RSs are available fortransmission in one RB according to the current specification and 16CSI-RSs are to be transmitted, the CSI-RSs are mapped to RBs. That is,since 8 CSI-RSs can be mapped to one RB, two RBs 600 and 610 are neededto map 16 CSI-RBs 620 and 630.

While the embodiment is similar to the embodiment disclosed in FIG. 5,the number of CSI-RSs to be mapped to one RB is fixed in system designand thus there is no need for signaling the number of CSI-RSs to bemapped per RB to the receiver.

[Table 7] illustrates an exemplary structure of a message in which thetransmitter transmits CSI-RS information to the receiver in anembodiment in which an RB bundle is used and a fixed number of CSI-RSsare mapped to one RB.

TABLE 7 CSI-RS-Config ::= SEQUENCE {  csi-RS      CHOICE {   release     NULL,   setup      SEQUENCE {    antennaPortsCount   ENUMERATED{an1, an2, an4, an8, an16,                      an32, an64},   resourceConfig     INTEGER (0. .31),    subframeConfig     INTEGER(0. .154),    p-C-r10        INTEGER (−8. .15)   }  } }

In the system according to the embodiment, the number of CSI-RSs to betransmitted in one RB by the transmitter is predetermined. Thetransmitter may indicate the total number of CSI-RSs to be transmitted,antennaPortsCount, and the receiver may determine the number of RBsneeded to receive the total CSI-RSs by dividing the total number ofCSI-RSs by the number of CSI-RSs mapped to one RB. According to themessage, the transmitter supports 16, 32, and 64 antenna ports, and thusmay add an16, an32, and an64 as values available as antennaPortsCount.

In the embodiment, since a predetermined number of CSI-RSs are mapped toall RBs, a new information element is not included in a message in whichthe transmitter transmits ZP-CSI-RS information to the receiver. Thatis, the ZP-CSI-RS information may be represented only by a ZP-CSI-RSidentifier (ID), a resource configuration, and a subframe configuration.

FIG. 7 illustrates a method for applying different CSI-RS mappings todifferent subframes using a plurality of CSI processors according to anembodiment of the present disclosure.

For example, a first CSI processor processes a horizontal antenna, andan RB 700 is one of RBs processed by the first CSI processor. The firstCSI processor may map CSI-RSs to RBs with an RB spacing of 2,F_(H-CSI-RS) 710 and an RB offset of 0 720. A second CSI processorprocesses a vertical antenna, and an RB 730 is one of RBs processed bythe second CSI processor. The second CSI processor may map CSI-RSs toRBs with an RB spacing of 3, F_(V-CSI-RS) 740 and an RB offset of 0 750.While FIG. 7 illustrates application of different RB mapping schemes todifferent subframes, it is also possible to apply two or more RB mappingschemes to one subframe.

The embodiment may be used as a method for applying the legacy mappingmethod and a plurality of embodiments of the present disclosure at thesame time. Specifically, the first CSI processor may use a mappingmethod that does not use an RB spacing or an RB bundle, and the secondCSI processor may use one of the mapping methods according to theembodiments of the present disclosure.

While the first and second CSI processors use only different RB spacingsin the mapping method of the embodiment, a mapping method for usingdifferent RB spacings (RB offsets) and RB bundle sizes according toprecoding utilization may be used. Further, some CSI processors may usea mapping method with an RB spacing and an RB offset, and other CSIprocessors may use a mapping method with an RB bundle.

FIG. 8 illustrates a method for applying different CSI-RS mappings inthe same subframe by applying the foregoing embodiments according to anembodiment of the present disclosure.

While different CSI-RS mapping schemes are applied to differentsubframes in FIG. 7, different CSI-RS mapping schemes may be applied inthe same subframe in FIG. 8.

For example, CSI-RSs 800 and 820 may be horizontal CSI-RSs (H-CSI-RSs),and CSI-RSs 810 and 830 may be vertical CSI-RSs (V-CSI-RSs). TheH-CSI-RSs are mapped with an RB spacing of 2 and an RB offset of 0, andthe V-CSI-RSs are mapped with an RB spacing of 2 and an RB offset of 1.The transmitter may transmit the H-CSI-RSs and the V-RSI-CSs in the samesubframe by generating a channel using a Kronecker product. In anotherexample, the CSI-RSs 800 and 820 may be CSI-RSs of a first BS, and theCSI-RSs 810 and 830 may be CSI-RSs of a second BS. That is, differentBSs may map CSI-RSs to RBs in the same subframe and transmit theCSI-RSs.

The foregoing embodiments may be applied in the same manner to channelstate information interference measurements (CSI-IMs) as well asCSI-RSs.

3GPP Release 12 regulates that one transmitter may map up to 8 CSI-RSsand up to 4 CSI-IMs to an RB. To reduce system overhead or to increasethe number of CSI-IMs without increasing system overhead, the aboveembodiments may also be applied to CSI-IMs.

The following description is given of an example of related parametersthat may be reflected in a CSI-IM configuration.

Specifically, [Table 8] illustrates an example of combining an RBspacing and an RB offset into one value D_(CSI-IM), and the results ofcombining RB spacings and RB offsets are same as listed in [Table 1].

TABLE 8 RB spacing and RB offset in combination RB offset (CSI-IM RB(CSI-RS-RBSpacingConfig) RB spacing offset) (D_(CSI-IM)) (F_(CSI-IM),RBs) (Δ_(F,CSI-IM)) 0 1 — 1-2 2 D_(CSI-IM)-1 3-5 3 D_(CSI-IM)-3 6-9 4D_(CSI-IM)-6 10-14 5 D_(CSI-IM)-10 15-20 6 D_(CSI-IM)-15

[Table 9] illustrates an exemplary structure of a message that thetransmitter transmits to the receiver, when a method for mapping CSI-RSsto RBs with an RB spacing to CSI-IMs.

TABLE 9   CSI-IM-Config ::= SEQUENCE {  csi-IM-ConfigId    CSI-IM-ConfigId,  resourceConfig    INTEGER (0. .31),  subframeConfig   INTEGER (0. .154),  D-CSI-IM      INTEGER (0. .20), }

Compared to [Table 2], it may be noted from [Table 9] that D-CSI-IM is aresult of combining an RB spacing and an RB offset, instead of D-CSI-RS.

FIG. 9 illustrates a method for applying the foregoing embodiments tomapping of CSI-RSs and CSI-IMs to RBs in the same subframe according toan embodiment of the present disclosure.

For example, RE groups 900 and 920 may carry CSI-RSs, and other REgroups 910 and 930 may carry CSI-IMs. The CSI-RSs may be mapped to theRBs with an RB spacing of 2 and an RB offset of 0, and the CSI-IMs maybe mapped to the RBs with an RB spacing of 2 and an RB offset of 1.

FIG. 10 is a diagram illustrating a signal flow between a BS and a UE,when embodiments of the present disclosure are applied.

A BS 1000 maps CSI-RSs to RBs in consideration of control ofinterference with a neighbor BS in operation 1004. That is, the BS 1000maps the CSI-RSs to the RBs at positions other than the positions of RBsto which CSI-RSs of the neighbor BS are mapped. Further, various RBmapping methods of the present disclosure may be applied.

The BS 1000 transmits a signal including CSI-RS mapping information to aUE 1002 in operation 1006.

The BS 1000 transmits the CSI-RSs mapped to the RBs to the UE 1002 inoperation 1008.

The UE 1002 performs channel estimation based on the mapped CSI-RSs inoperation 1010.

The UE 1002 feeds back at least one of a rank indication (RI), aprecoder matrix indication (PMI), and a channel quality indication (CQI)to the BS 1000 based on the channel estimation in operation 1012.

FIG. 11 is a block diagram of a transmitter according to the presentdisclosure.

A transmitter 1100 according to the present disclosure is an apparatusthat maps CSI-RSs to RBs and transmits the CSI-RSs, and performs themethods (or operations) of a transmitter described in the presentdisclosure. For example, the transmitter 1100 may be a BS, an eNB, orthe like in a cellular system.

The transmitter 1100 may include a transceiver 1102 for transmitting andreceiving signals to and from a receiver, and a controller 1104 forcontrolling the transceiver 1102.

The controller 1104 may be understood as performing all operationsaccording to an embodiment for a transmitter according to the presentdisclosure.

While the transceiver 1102 and the controller 1104 are shown as separatecomponents in FIG. 11, the transceiver 1102 and the controller 1104 maybe incorporated into a single component.

FIG. 12 is a block diagram of a receiver according to the presentdisclosure.

A receiver 1200 according to the present disclosure is an apparatus thatreceives CSI-RSs mapped to RBs, and performs the methods (or operations)of a receiver described in the present disclosure. For example, thereceiver 1200 may be a UE or the like in a cellular system.

The receiver 1200 may include a transceiver 1202 for transmitting andreceiving signals to and from a transmitter, and a controller 1204 forcontrolling the transceiver 1202.

The controller 1204 may be understood as performing all operationsaccording to an embodiment for a receiver according to the presentdisclosure.

For example, when receiving RSs in an embodiment using an RB spacing,the controller 1204 may receive a message indicating a spacing betweentwo RBs to which RSs are mapped and an RB offset indicating thepositions of the RBs to which RSs are mapped. The controller 1204 mayreceive the RSs using the spacing and RB offset indicated by themessage, and perform channel estimation using the received RSs. Herein,the controller 1204 may receive the RSs in transmission resourcesconfigured to include at least one RB without RSs between the two RBs towhich RSs are mapped. The controller 1204 may feed back the result ofthe channel estimation to the transmitter.

For example, if receiving RSs in an embodiment using RB bundling, thecontroller 1204 may receive a message indicating the maximum number ofantenna ports used for RS transmission. The controller 1204 may receivethe RSs based on the maximum number of antenna ports indicted by themessage and perform channel estimation using the received RSs. Herein,the controller 1204 may receive the RSs in transmission resources mappedto at least two contiguous RBs to which at least two different RSsubsets of the RSs are mapped in a subframe. The controller 1204 mayfeed back the result of the channel estimation to the transmitter.

While the transceiver 1202 and the controller 1204 are shown as separatecomponents in FIG. 12, the transceiver 1202 and the controller 1204 maybe incorporated into a single component.

The above-described operations may be implemented by providing a memorystoring a related program code in a component of a transmitter (BS) or areceiver (UE) in a communication system. That is, a controller of thetransmitter or the receiver may perform the above-described operationsby reading and executing the program code stored in the memory by meansof a processor or a central processing unit (CPU).

Various components and modules of a transmitter or a receiver asdescribed in the present disclosure may operate in hardware circuitssuch as complementary metal oxide semiconductor (CMOS)-based logiccircuits, firmware, software, and/or a combination of hardware andfirmware and/or software inserted into a machine-readable medium. Forexample, various electrical structures and methods may be implemented byuse of electrical circuits such as transistors, logic gates andapplication-specific integrated circuits (ASICs).

While the disclosure has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the disclosure asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for transmitting a channel stateinformation reference signal (CSI-RS) in a wireless communicationsystem, the method comprising: transmitting information on CSI-RSresource mapping, the information on the CSI-RS resource mappingincluding information related to at least one resource block (RB) towhich a CSI-RS is not mapped, wherein the at least one RB is locatedbetween two RBs to which the CSI-RS is mapped respectively, and whereinthe at least one RB is located between the two RBs in a frequencydomain; and transmitting the CSI-RS based on the information on CSI-RSresource mapping.
 2. The method of claim 1, wherein the information onthe CSI-RS resource mapping includes information on one or more resourceelements (REs) per an RB, each of the one or more REs mapped to a CSI-RSport.
 3. The method of claim 1, wherein the information on CSI-RSresource mapping includes information indicating an RB offset, andwherein the RB offset indicates which RBs are occupied by the CSI-RS. 4.The method of claim 3, wherein the RB offset indicates positions of thetwo RBs to which the CSI-RS is mapped.
 5. The method of claim 1, whereinthe information on CSI-RS resource mapping includes information of zeropowered CSI-RS (ZP-CSI-RS) resources.
 6. A method for receiving achannel state information reference signal (CSI-RS) in a wirelesscommunication system, the method comprising: receiving information onCSI-RS resource mapping, the information on the CSI-RS resource mappingincluding information related to at least one resource block (RB) towhich a CSI-RS is not mapped, wherein the at least one RB is locatedbetween two RBs to which the CSI-RS is mapped respectively, and whereinthe at least one RB is located between the two RBs in a frequencydomain; and receiving the CSI-RS based on the information on CSI-RSresource mapping.
 7. The method of claim 6, wherein the information onthe CSI-RS resource mapping includes information on one or more resourceelements (REs) per an RB, each of the one or more REs mapped to a CSI-RSport.
 8. The method of claim 6, wherein the information on CSI-RSresource mapping includes information indicating an RB offset, andwherein the RB offset indicates which RBs are occupied by the CSI-RS. 9.The method of claim 8, wherein the RB offset indicates positions of thetwo RBs to which the CSI-RS is mapped.
 10. The method of claim 6,wherein the information on CSI-RS resource mapping includes informationof zero powered CSI-RS (ZP-CSI-RS) resources.
 11. An apparatus fortransmitting a channel state information reference signal (CSI-RS) in awireless communication system, the apparatus comprising: a transceiverconfigured to: transmit information on CSI-RS resource mapping, theinformation on the CSI-RS resource mapping including information relatedto at least one resource block (RB) to which a CSI-RS is not mapped,wherein the at least one RB is located between two RBs to which theCSI-RS is mapped respectively, and wherein the at least one RB islocated between the two RBs in a frequency domain; and transmit theCSI-RS based on the information on CSI-RS resource mapping.
 12. Theapparatus of claim 11, wherein the information on the CSI-RS resourcemapping includes information on one or more resource elements (REs) peran RB, each of the one or more REs mapped to a CSI-RS port.
 13. Theapparatus of claim 11, wherein the information on CSI-RS resourcemapping includes information indicating an RB offset, and wherein the RBoffset indicates which RBs are occupied by the CSI-RS.
 14. The apparatusof claim 13, wherein the RB offset indicates positions of the two RBs towhich the CSI-RS is mapped.
 15. The apparatus of claim 11, wherein theinformation on CSI-RS resource mapping includes information of zeropowered CSI-RS (ZP-CSI-RS) resources.
 16. An apparatus for receiving achannel state information reference signal (CSI-RS) in a wirelesscommunication system, the apparatus comprising: a transceiver configuredto: receive information on CSI-RS resource mapping, the information onthe CSI-RS resource mapping including information related to at leastone resource block (RB) to which a CSI-RS is not mapped, wherein the atleast one RB is located between two RBs to which the CSI-RS is mappedrespectively, and wherein the at least one RB is located between the twoRBs in a frequency domain; and receive the CSI-RS based on theinformation on CSI-RS resource mapping.
 17. The apparatus of claim 16,wherein the information on the CSI-RS resource mapping includesinformation on one or more resource elements (REs) per an RB, each ofthe one or more REs mapped to a CSI-RS port.
 18. The apparatus of claim16, wherein the information on CSI-RS resource mapping includesinformation indicating an RB offset, and wherein the RB offset indicateswhich RBs are occupied by the CSI-RS.
 19. The apparatus of claim 18,wherein the RB offset indicates positions of the two RBs to which theCSI-RS is mapped.
 20. The apparatus of claim 16, wherein the informationon CSI-RS resource mapping includes information of zero powered CSI-RS(ZP-CSI-RS) resources.